1. Field of the Invention
The present invention relates to a tube for a rubber boat which is provided at the side portions of a rubber boat and whose intended expanded configuration is a substantially cylindrical configuration having a predetermined three-dimensional curve as the central line thereof, and to a method of fabricating the tube for a rubber boat.
2. Description of the Related Art
Generally, rubber boats are formed by a boat main body which is made of rubber, a boat bottom which is installed at a bottom portion of the boat main body, and the like. The boat main body includes the bottom portion, at which the boat bottom is installed, and expanding tubes, which are provided at the side portions of the bottom portion and which provide buoyancy.
The tubes are formed on the whole as substantial cylinders, but are not formed as straight cylinders. Namely, the portions of the tubes which form the side portions of the bottom portion are substantial parallel cylinders which run along the keel line, but toward the bow, the tubes are provided in tapered configurations which gradually curve toward the keel line.
In general, there are two methods of fabricating such tubes. In the first method of fabrication, a plurality of cylindrical tube elements and truncated cone-shaped elements are prepared, and these elements are successively connected together. This first method of fabrication is the more frequently used method. In the second method of fabrication, two sheet materials are readied and fit together. In this state, the sheet materials are cut into predetermined curved configurations, and are then adhered together. This second method of fabrication is used for small rubber boats having flat bottoms.
However, the work involved in the first method of fabrication is complex as the cylindrical tube elements and the truncated cone-shaped tube elements must be successively connected together. Further, when the tubes are expanded, there are folds at the connections of the respective elements at portions toward the bow, and accordingly, the quality of tile external appearance deteriorates. In the second method of fabrication, tubes having a good external appearance which curve smoothly are obtained. However, there is a drawback in that only a two-dimensional curved configuration can be realized (the tubes are of configurations which curve when viewed from above, but do not curve when viewed from the sides).
In recent years, rubber boats for improving the ability to ride over waves and seaworthiness, which rubber boats have a three-dimensional boat body configuration, have been used. Accordingly, tubes having configurations which curve three-dimensionally (configurations which curve when viewed from above and from the sides) are necessary. In this case, the first method of fabrication can be used, but, as mentioned above, the operations involved therein are complex and the external appearance of the boat deteriorates.